1. Field of the Invention
The present invention relates to a method of manufacturing a sliding part, and a vortex flow generator for an injection valve manufactured by that method.
2. Description of the Related Art
FIG. 2 is a sectional view showing a fuel injection valve 1 for injecting a fuel into a cylinder (hereafter referred to simply as the injection valve, when applicable), and FIG. 3A and FIG. 3B are a sectional view and a plane view, each showing a vortex member (a sliding part or a vortex flow generator) 13 incorporated in a valve device 3 of the injection valve 1.
As shown in FIG. 2, the injection valve 1 includes a housing main body 2, and the valve device 3 fixed to one end of the housing main body 2 by caulking or the like and covered by a sleeve 35. A fuel supply tube 4 is connected to the other end of the housing main body 2 so that a high pressure fuel is supplied from the fuel supply tube 4 through a fuel filter 37 to the injection valve 1.
The housing main body 2 includes a first housing 30 having a flange 30a through which the injection valve 1 is mounted onto a cylinder head (not shown) of an internal combustion engine, and a second housing 40 onto which a solenoid device 50 is mounted. The solenoid device 50 has a bobbin 52 on which a coil 51 is wound, and a core 53 installed in an inner circumferential portion of the bobbin 52. A winding of the coil 51 is connected to a terminal 56. The core 53 is formed into such a hollow cylindrical shape so as to define a fuel passage therein. A spring 55 is provided in the hollow portion of the core 53 and compressed between an adjuster 54 and a needle valve 12. An armature 31 is attached integrally to the other end of the needle valve 12 to confront with the leading end of the core 53. The intermediate portion of the needle valve 12 is formed to have a guide 12a for slidingly guiding the valve 12 along the inner circumferential surface of a valve main body 9, and a needle flange 12b contacted with a spacer 32 installed in the first housing 30. The housing main body 2 and the sleeve 35 cooperatively constitute a housing of the injection valve 1.
The first housing 30, the core 53 and the armature 31 are made of magnetic material, such as an electromagnetic stainless, to form a magnetic circuit.
The valve device 3 includes the valve main body 9, a valve seat 11, the needle valve 12 and the vortex member 13. The valve main body 9 is formed into a stepped hollow cylindrical shape, which has a central hole 9a axially-slidably and concentrically supporting the needle valve 12 while circumscribing the guide 12a of the same, and an accommodation hole 9b formed by enlarging the diameter of the leading end side of the central hole 9a for accommodating the valve seat 11 and the vortex member 13 therein. The valve seat 11 has a fuel injection hole 1 at its center, and is fixedly provided within the accommodation hole 9b of the valve body 9. The needle valve 12 is brought into and out of contact with the valve seat 11 by the solenoid device 50 to close and open a fuel injection hole 10. The vortex member 13 serves as the sliding member for guiding the needle valve 12 in an axial direction, and applying a vortex motion to the fuel before the fuel flows into the fuel injection hole 10 of the valve seat 11 radially inwardly.
A structure of the vortex member 13 will be described in detail with reference to FIGS. 3A and 3B.
The vortex member 13 is substantially in the form of a hollow cylindrical shape, which has a central hole 15 concentrically and axially-slidably supporting the needle valve 12 while surrounding the same. The vortex member 13 has a first end face 16 to be contacted with the valve seat 11, a second end face 17 opposite from the valve seat 11, and a periphery 18 contacted with the inner circumferential surface of the accommodation hole 9b of the valve main body 9, when assembled into the valve device 3.
The second end face 17 of the vortex member 13 is contacted with and supported by a stepped portion 9c of the accommodation hole 9b of the valve main body 9, is formed with passage grooves 17a each extended radially to allow the fuel to flow from the inner circumferential portion of the second end face 17 to the outer circumferential portion thereof. The periphery 18 of the vortex member 13 is formed with a large number of planar surfaces, which are provided at constant angular intervals in the circumferential direction and extends in the axial direction. More specifically, the periphery 18 is formed with a plurality of outer peripheral portions 18a in contact with the inner circumferential portion of the accommodation hole 9b of the valve main body 9 for regulating the relative position of the vortex member 13 to with respect to the valve main body 9, and flow passage portions 18b each of which is in the form of a planar surface located between adjacent two outer peripheral portions 18a and defines an axial flow passage for the fuel in cooperation with the inner circumferential surface of the accommodation hole 9b. Provided in the first end face 16 of the vortex member 13 are an inner circumferential annular groove 16a, which has a predetermined width and is formed in the inner circumferential portion adjacent to the central hole 15, and vortex grooves 16b each of which extends substantially radially inwardly so that one end thereof is connected to the flow passage portion 18b of the periphery 18 whereas the other end thereof is connected to the inner circumferential annular groove 16a in a tangential direction.
This valve device 3 is assembled as follows: The vortex member 13 is inserted into the accommodation hole 9b through one end of the valve main body 9, then the valve seat 11 is pressure-inserted into the accommodation hole 9b through the one end of the valve main body 9 and thereafter the valve main body 9 and the valve seat 11 are welded together for integration in an airtight manner. Further, the needle valve 12 is inserted into the central hole 9b through the other end of the valve main body 9 so that the leading end of the needle valve 12 is inserted into the central hole 15.
In the valve device 3, the needle valve 12 is reciprocally moved in the axial direction by the action of the solenoid device 50 such that the guide 12a is slide along the inner circumferential surface of the central hole 9a of the valve main body 9 and the leading end side of the needle valve 12 is slide along the inner circumferential surface of the central hole 15. The fuel injection hole 10 is closed when the leading end of the needle valve 12 is seated on the valve seat 11. During the opening of the fuel injection hole 10, the fuel passes through the passage grooves 17a to flow between the inner circumferential surface of the accommodation hole 9b and the flow passage portions 18b, and then passes through the vortex grooves 16b to flow into the inner circumferential annular grooves 16a in the tangential directions, thereby forming the vortex flow entering into the fuel injection hole 10 and dispersed from the leading end outlet thereof.
The injection valve 1 thus constructed is mounted in such a manner than the leading end thereof is inserted into an injection valve insertion hole (not shown) provided in the cylinder head, a depressing metal is applied to the flange 30 downwardly, and the depressing metal is fixedly tightened to the cylinder head with mounting bolts (not shown). Here, a planar washer or a corrugated washer is interposed between the injection valve 1 and the cylinder head, and the axial depressing force by the depressing metal ensures the sealing between the injection valve 1 and the cylinder head. In addition, the fuel supply tube 4 is fixed such that its attaching hole is engaged with an O-ring portion for sealing the upper portion of the injection valve 1.
By the control for the energization of the coil 51, the needle valve 12 is moved axially to open and close the fuel injection hole 10.
When the fuel injection hole 10 is opened, the fuel is supplied from the fuel supply tube 4, allowed to pass through the fuel passage inside the core 53, given vortex energy with the aid of the vortex member 13, and then dispersed from the fuel injection hole 10 into a combustion chamber.
This vortex member 13 is complicated in configuration. The grooves, which give or apply the vortex energy to the fuel, require extremely high accuracy in order to suppress variations in fuel injection quantity and dispersed configuration as small as possible. Further, anti-friction property is required for the central hole 15. For these reasons, the vortex member 13 must be manufactured with high dimensional accuracy from material having anti-friction property and high hardness, such as SUS440C. In general, the vortex member 13 is manufactured by machining (cutting), metal injection molding, sintering, cold forging or the like.
Manufacturing the vortex member 13 by the machining makes it easy to attain the required high dimensional accuracy, but difficult to cope with the complicated configuration, and results in the increased cost to manufacture.
Manufacturing the vortex member 13 by sintering or cold forging makes it easy to attain the complicated configuration but difficult to attain the high dimensional accuracy.
For these reasons, an attempt has been made to manufacture the vortex member 13 by metal injection molding which is advantageous over the machining in cost and applicability of the complicated configuration and by which high dimensional accuracy is available in contrast to the sintering and the cold forging.
However, iron-base alloys containing Cr of 10-20% and C of 0.5% or more such as SUS440C, which are superior in anti-friction and anti-corrosion properties, have liquid-phase line around 1260.degree. C., and thus the upper limit of baking temperature is predetermined. Further, face-centered cubic phase appears in a range from 800.degree. C. to the liquid-phase line, and thus sintering is hard to develop. Accordingly, the high dimensional accuracy cannot be attained by a conventional powder metallurgy in which a partially-low-density compacted member is baked.
Further, variation in carbon content of the baked member is large in case of a conventional baking process which does not accompany ambient adjustment, and it is not rare that carburizing process is required to adjust the carbon content to a desired value. Consequently, variation in hardness after thermal processing is unavoidable.
Therefore, a manufacturing method used in the conventional metal powder metallurgy encounters the difficult in processing SUS440C to provide high dimensional accuracy, high hardness and low porosity.